How Stonehenge Worked

Eight miles (13 kilometers) north of Salisbury in Wiltshire, England, U.K., lies Stonehenge — an enormous circle of stones. It's an ancient monument that was of great significance to the people who erected it. Unfortunately, we don't know what that significance was, nor do we know much about the prehistoric people who built it. The mystery of Stonehenge has intrigued us for centuries, but until the 20th century, we didn't even know how old the whole thing was.

But every visitor knows the obvious: The society responsible for it went to a lot of trouble to put it up. It clearly required planning, organization, cooperation and manpower.

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Archaeologists now estimate that an ancient society transported the stones from a great distance and erected the larger stones between 2620 and 2480 B.C.E. [source: Pearson]. It's still a mystery how these Britons transported such large stones, especially before the invention of the wheel. Experts have proposed several theories as to how humans could have transported the stones from so far, including the use of log rollers, stone ball bearings, or small rocks and rotation, or even wicker cages [source: Cohen].

But we also know that these stones are just one piece of the puzzle. Stonehenge sits in the middle of an older archaeological site consisting of a ditch and bank. Here, archaeologists have found cremated remains of more than 60 humans, in addition to some unburned human bones and many animal remains [source: Pearson]. Plus, this site is just one of many important ancient finds across the surrounding landscape, which was dotted with other monuments centuries ago.

To put the story in context, keep in mind that the Egyptians erected their famous pyramids during the same centuries in which the Britons erected Stonehenge. Civilizations were flourishing in the Middle East, but Britons remained in the Stone Age (specifically, the Neolithic, meaning New Stone Age) as the technology of metalworking slowly crept farther into Europe. Although these Britons weren't primitive hunter-gatherers (they were farmers who lived on barley and wheat), they probably valued the open valley where Stonehenge stands as a convenient hunting ground.

A wealth of new research over the past 15 years has unlocked new secrets to Stonehenge and its place among other long-vanished monuments. First, let's examine the monument itself.

This lintel stone shows how Stonehenge's builders attached it to its neighbors.

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The most remarkable part of Stonehenge is its larger upright stones, called sarsens. Sarsen is a particular kind of sandstone rock, and the closest source of such stone is Marlborough Downs, about 20 miles (32 kilometers) away from Stonehenge. Lintels are the long sarsen rocks that lie horizontally atop two vertical sarsens.

When they were all standing, the inner sarsens would've formed a horseshoe shape with five stand-alone trilithons, which consist of two vertical sarsens topped with a lintel sarsen. The largest trilithon (30 feet or 9 meters tall) would have stood at the bottom of the horseshoe, but it's now partially collapsed. The average weight of one of these sarsens is more than 49,800 pounds (22.6 metric tons) [source: English-Heritage.org].

The ancient Britons carefully shaped these hard stones. They carved mortise holes into the underside of the lintels that fit snugly on protruding points called tenons carved into the top of the vertical sarsens. Tenons and mortise holes are typically used only in woodworking, suggesting the feature was symbolic. The lintels along the outer circle, likewise, fit snugly together end-to-end with a tongue-and-groove connection. This outer circle is far from complete, but enough stones stand to make it clear what the planners probably intended: a complete circle about 108 feet (33 meters) across, consisting of 30 vertical sarsens and 30 lintels. Four more sarsen stones, known as the Slaughter Stone, the enormous Heel Stone and two Station Stones, sit outside the outer sarsen circle.

The smaller stones that sit within the sarsen circle are called bluestones because they look blue when wet or freshly cut, and each weighs 4,409 to 11,023 pounds (2 to 5 metric tons) [source: English-Heritage.org]. The bluestones aren't just one type of rock: 30 are basaltic dolerite, five consist of igneous rhyolite, five are other types of volcanic rock and three are sandstone [source: Lambert]. As such, they also came from different sources. Geological analysis suggests that at least 11 came from the Preseli Hills in western Wales (140 miles or 225 kilometers away), but others possibly came from more local sources [source: Lambert].

Many of these bluestones sit in a circle between the horseshoe of trilithons and the outer circle, while another set is arranged in an oval shape within the horseshoe. The "Altar Stone," made of Welsh sandstone (different from the sarsens), weighs more than 17,600 pounds (8 metric tons) and lies underneath the fallen sarsen of the biggest trilithon [source: Pearson].

Though covered with grass, the original ditch ancient Britons dug around the Stonehenge site is still clearly visible.

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Experts believe ancient Britons prized the Salisbury Plain as a convenient hunting ground. In addition, a natural causeway created by glacial heaving and thawing formed a grooved "avenue" that coincided with the rising of the summer solstice sun as it leads up to the current Stonehenge site. While today we understand this as a natural coincidence, these ancient peoples could have considered it a sacred place divinely designed.

During the first phase of building Stonehenge, in approximately 3000 B.C.E., ancient Britons used deer antlers to dig a ditch along the perimeter of a circular enclosure about330 feet (100 meters)across, with a high bank on the inside of the circle and a low bank on the outside [source: Pearson]. The "henge" in Stonehenge refers to this earthen enclosure that was unique to ancient Britain. We know of about 50 certain henges in existence [source: Last]. However, the ditch that encloses Stonehenge isn't a true henge. Instead, it's backward; a true henge has a ditch on the inside of a bank [source: Pearson].

The designers left one wider entrance on the circle's northeast end, leading toward the avenue, and one narrower entrance on the south side. In the 17th century, antiquarian John Aubrey identified 56 holes along the inside perimeter of the circle [source: Pearson]. These "Aubrey Holes" could've held wood posts or perhaps bluestones. Other archaeologists have discovered cremated human remains in and around these holes — likely placed there over the next several centuries after the trench was dug. Archaeologists have also discovered numerous other postholes inside the ditch, suggesting perhaps that wooden structures stood there or that the posts themselves mapped astronomical movements. Archaeologists believe the Britons could have erected the Heel Stone during this first phase or perhaps earlier.

The next stage of Stonehenge's development occurred between 2620 and 2480 B.C.E., when the ancient Britons erected the sarsen horseshoe and outer circle [source: Pearson]. They meticulously shaped the sarsen stones to fit the desired design of the monument, with tapered upright sarsens and a remarkably level surface along the top of the lintels in the outer sarsen circle.

Around 2300 B.C.E., the ancient Britons also dug ditches and banks along the borders of the avenue leading to Stonehenge [source: Pearson]. The avenue was about 40 feet (12 meters) wide and 1.7 miles (2.8 kilometers) long and followed an indirect route to the River Avon [source: Pearson]. Over the next several centuries, the bluestones were repositioned to where they are now, presumably to fit new purposes of a changing society.

Fellow Neolithic henge Avebury sits about 19 miles north of Stonehenge.

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Although Stonehenge itself is the most well-known relic of the Neolithic, Britain — and especially the landscape immediately surrounding Stonehenge — is rich in archaeological discoveries:

In preparation for laying a parking lot for Stonehenge visitors in the 1960s, archaeologists discovered three postholes, which held pine poles (possibly totems) all dating to the eighth millennium B.C.E., about 650 feet (200 meters) from the Stonehenge site [source: Pearson]. Experts marveled at the idea of Mesolithic hunter-gather societies erecting monuments.

During the fourth millennium B.C.E. in Salisbury Plain, ancient Britons built 17 long barrows, earthen enclosures of wood or stone, to house the dead. Thousands of years later, between 2200 and 1700 B.C.E., the area remained important, as the ancient Britons built more than 1,000 additional round barrows [source: Pearson].

Also in the fourth millennium B.C.E, people were building causewayed enclosures, such as Robin Hood's Ball, 3 miles (4 kilometers) northwest of what would become the Stonehenge site [source: Pearson]. (Despite its name, it has nothing to do with the medieval hero.) Such enclosures consist of an earthen ditch and bank with entryways, which probably marked gathering places for ceremonies [source: Pearson].

In the 18th century, Antiquarian William Stukeley discovered what he thought looked like a Roman racetrack, so he called it the Cursus. The Cursus is a 1.75-mile (2.8-kilometer) long enclosure consisting of a bank and outer ditch (like Stonehenge) [source: Pearson]. Another much smaller cursus, called Lesser Cursus, sits close by to the northeast of the Greater Cursus. Archaeologists also date these to the fourth millennium B.C.E. but are still unsure of their purpose [source: Pearson].

Durrington Walls is an ancient henge encompassing 42 acres (0.17 square kilometers) just two miles (3.2 kilometers) northeast of Stonehenge. The bank and ditch once stood around 10 feet (3 meters) high and 18 feet (5.5 meters) deep [source: Pearson]. It contained two timber circles about the size of Stonehenge that archaeologists believe were temporary settlements for Stonehenge's builders. Just south of Durrington Walls stood another timber circle called Woodhenge.

About 18.5 miles (30 kilometers) north is Avebury, an enormous henge containing a circle of sarsen stones dating from 2850 to 2200 B.C.E [source English-Heritage.org].

In 2008, archaeologists excavated the end of the Stonehenge avenue before the river. What they found was Bluestonehenge, a henge 30 feet (10 meters) wide with holes that were possibly the original homes for Stonehenge's bluestones [source: Pearson]. Archaeologists date the henge to the 23rd century B.C.E. (around the same time the ditches along the avenue were dug), but the stones were probably placed there before 2500 B.C.E. [source: Pearson].

The theory that Druids built Stonehenge originally surfaced in the 17th century. Today, people calling themselves Druids visit Stonehenge to celebrate events like the Summer Solstice.

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Many questions still surround Stonehenge, including whether it was ever finished and what purposes it served throughout time. But archaeologists have been able to debunk many of the old popular theories.

One of the oldest origin stories we know of comes from 12th-century cleric Geoffrey of Monmouth in his book "Historia Regum Britanniae" ("History of the Kings of Britain"). He writes that giants originally brought the stones from Africa and erected them in Ireland, where it was known as "the Giant's Dance" with special healing powers. To commemorate the deaths of 460 Britons who died in battle against the Saxons, the fabled wizard Merlin suggested stealing the Giant's Dance. Merlin brought 15,000 men on the mission, but after they defeated the Irish defense, the men couldn't move the stones. Naturally, Merlin employed magic to load them on the boats [source: Monmouth].

Some scholars believe Geoffrey of Monmouth didn't invent the story, but simply recounted known folklore, while many other experts doubt an oral folktale could've survived from the Neolithic. Regardless, the account aligns with the theory that Stonehenge was meant to honor the dead and that the stones were originally believed to have unique healing powers.

In the early 17th century, King James I commissioned an excavation in the center of Stonehenge, but his workers found only animal bones and burnt coals. An architect, Inigo Jones, surveyed the monument and guessed it was the work of the Romans. Later that century, however, John Aubrey (aforementioned discoverer of holes) theorized that Stonehenge was a pagan temple, and therefore attributed it to the Druids. The Druids were a secretive Celtic cult of pagan priests thriving from the third century B.C.E. until the Romans suppressed them in C.E. 61.

In the 18th century, antiquarian William Stukeley offered some insight that supported Aubrey's Druid theory. He became the first to note the alignment of Stonehenge with the sunrise on the summer solstice (the longest day of the year), and therefore, the sunset on the winter solstice (the shortest day of the year). For many, this revelation shed light on the original purpose of Stonehenge, which could've been a temple to the sun. After all, the Druids had studied astronomy. However, modern dating techniques employed in the 20th century dated Stonehenge to well before the Druids.

In 1963 Gerald Hawkins published a best-seller declaring Stonehenge to be a calendar and predictor of eclipses. Archaeological experts accept the theory that it marked solstices intentionally, but they remain skeptical that the monument was built for astronomical capabilities beyond that [source: Pearson].

More recent theories about Stonehenge revolve around its use as a burial site.

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In the first decade of the 2000s, archaeologist Mike Parker Pearson led the Stonehenge Riverside Project, which was responsible for the research and excavations that have shed so much new light on Stonehenge and its builders. Thanks to the new information, Pearson and others have crafted new theories that might explain Stonehenge and its original purposes.

Pearson theorizes that Stonehenge was a place of the dead in the same way that Durrington Walls was a place of the living. The discovery of timber circles and another natural "avenue" made of broken flint leading from the River Avon to the southern circle in Durrington Walls supports this theory. Pearson also points out that Durrington was mostly filled with animal remains from feasting, whereas Stonehenge has a higher concentration of human remains. In addition, the mortise-holes-and-tenons feature of the outer Stonehenge circle is a feature typical of woodworking and unnecessary for the stone monument, suggesting its symbolic imitation of a house for the living.

However, Stonehenge wasn't a burial site for just anybody. It was probably meant just for an elite group. Pearson notes that the cremated remains include a high proportion of men. He also argues that the discoveries of a polished stone mace head and incense burner among the remains suggest the buried individuals were political and religious leaders.

Another theory considers Stonehenge a monument to unification. The Britons were of diverse ancestry, building Stonehenge at a time when tribal people blended at peace with one another. It was possibly symbolic to bring bluestones from a place of Welsh ancestry together with British sarsens. The monument's orientation suggests a cosmic unification of the earth, sun and moon [source: Pearson].

Others point to the high occurrence of injury and illness in the burial remains around Stonehenge. This could suggest that Stonehenge was a place of healing. Steven Waller, a specialist in archaeoacoustics, speculates that the ancient Britons were inspired to erect the stones by the phenomenon of noise-cancelling effects that happen when two pipers play in a field. Waller connects this with one folk origin story having to do with pipers leading maidens to the field and turning them to stone [source: Pappas].

Considering that the ancients rearranged bluestones several times over centuries and many of the sarsens are missing or perhaps never even made it to their final resting place, we might never know the true purpose of Stonehenge. Yet, what we have found out about the monument has been a fascinating glimpse into prehistoric society and its impressive accomplishments.

Glacial Deposits

One theory states that the builders didn't need to transport the bluestones far; rather, glacial activity from the last ice age deposited the stones in Salisbury Plain. Most of today's archaeologists disagree with this theory, however, asserting the stones were moved thanks to human effort [source: English-Heritage.org]. Pearson states that modern geological evidence shows the rocks couldn't have been transported as far as Salisbury Plain, and the closest they could have come would have been 40 miles (64 kilometers) away [source: Pearson].

Author's note: How Stonehenge Worked

I've always had the vague idea that Stonehenge was an impressive prehistoric monument and that archaeologists have little knowledge of how it was erected. But I'm embarrassed that I didn't know how much we have found out about Stonehenge in the past few decades. For those like me who don't actively follow archaeological news, it's eye opening to return to a subject and discover how quickly modern ideas about it have changed. Here's hoping we can continue to advance our technological and archaeological methods to discover more about ancient civilizations.